What is the definition of what a medium mass star becomes at the end of it's life?

At the end of its life, a medium mass star, typically between about 1 to 8 times the mass of the Sun, evolves into a red giant and ultimately sheds its outer layers, creating a planetary nebula. The remaining core, which is primarily composed of carbon and oxygen, becomes a white dwarf. This white dwarf gradually cools and fades over time, eventually becoming a cold, dark remnant known as a black dwarf, although the universe has not yet had enough time for any black dwarfs to form.